In European patent application 80101949.8, Robert Bosch GmbH specifies an apparatus and method for testing of rechargeable batteries in varying states of charge. The Bosch reference, however, discloses a method having inherent limitations that would result in a battery tester having several disadvantages and problems. These disadvantages and problems will become apparent to one of skill in the art through comparison of the Bosch reference with the present invention as set forth in the remainder of the present application with reference to the drawings.
Various aspects of the present invention can be found in a rechargeable energy storage battery testing system that measures the open circuit voltage and a dynamic parameter of a test battery, scales the measured dynamic parameter, and determines the physical condition of the test battery using the open circuit voltage, the scaled dynamic parameter and correlation data. The system then displays to a test operator the physical condition of the test battery.
The correlation data used to calculate the physical condition may be stored in system memory, and is based on the dynamic parameter of another standard battery (or batteries) at one or more charge states. The scaling of the dynamic parameter is based on the same dynamic parameter of a standard battery that corresponds to the test battery, and may be carried out by multiplying the measured dynamic parameter of the test battery by the ratio of the ratings of the test battery and a battery upon which the correlation data is based. The dynamic parameter used may be, for example, the internal alternating current resistance, or, alternatively, conductance, impedance or admittance.
In one embodiment of the invention, the system applies a high current load pulse to the test battery, and then waits a predetermined rest period before measuring the open circuit voltage.
In another embodiment, the correlation data is based on a single charge state, and the system determines whether the physical condition of the test battery falls below the correlation data. If it does, the system indicates that the test battery has failed, which indication may be carried out by displaying an xe2x80x9cFxe2x80x9d or xe2x80x9cFailxe2x80x9d condition. Otherwise, the system indicates that the battery has passed, which again may be carried out by displaying a xe2x80x9cPxe2x80x9d or xe2x80x9cPassxe2x80x9d condition.
In a further embodiment of the invention, the system also (or alternatively) determines the charge state of the test battery, and displays the charge state to a test operator. The charge state may be determined from a calculated state of charge value for the test battery. For example, the system may analyze the calculated state of charge value and determine within which of several value ranges the calculated state of charge value falls. Since each of the value ranges represents a different charge state, the range determined also determines the charge state of the test battery.
The state of charge value may be determined using the measured open circuit voltage and the correlation data. For example, in one embodiment, the correlation data represents an open circuit voltage versus amp hour removed curve. The measured open circuit voltage is compared to the open circuit voltage represented by the correlation data, and the number of data points compared is counted until the measured open circuit voltage becomes greater than or equal to the open circuit voltage represented by the correlation data. The number of points compared is then divided by the total number of points in the curve, and the result represents the relative distance along the curve. The result is then subtracted from one to obtain the state of charge value.
Other aspects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.